I've encountered chat lag occasionally before but never like this. The weirdest symptom is: I find that the Shift key applies to the letter that's appearing on the screen right at the moment, and not to the letter that I actually shifted, which means that the slow-appearing letters are shifted "too soon". For example, if I want to type: Look out! Rook attack!, the letters poke out at like 300 baud but the Shift key applies in real time, so what actually appears is LooKOut1 rook attack! It makes me look like a nine-year-old kid :p
This has been happening a lot since Thursday (I feel like it started happening around the feat, but never stopped even after multiple reloads). On my home computer I use Firefox 15.0.1 with Flash 11.4.402.278, which seems to be the latest; it happens at work too, where I use an older version of FF.